Communication system providing hybrid optical/wireless communications and related methods

ABSTRACT

A communication system includes at least one optical-wireless device coupled to a longitudinal side of an optical fiber. The optical-wireless device may include an optical fiber power unit for converting optical power into electrical power, and a wireless communication unit electrically powered by the optical fiber power unit. The optical-wireless device may include a substrate mounting the optical fiber power unit and the wireless communication unit to the longitudinal side of the optical fiber. The wireless communication unit may include a radio frequency transmitter, and a signal optical grating coupling the transmitter to the longitudinal side of the optical fiber. The radio frequency transmitter in some embodiments may include an ultra-wideband transmitter. A dipole antenna may also be provided including first and second portions extending in opposite directions along the longitudinal side of the optical fiber.

FIELD OF THE INVENTION

The present invention relates to the field of communications, and, moreparticularly, to a communication system, devices and associated methodsfor hybrid optical/wireless communications and conversions.

BACKGROUND OF THE INVENTION

Communications systems are often used to route data, voice, and/or videosignals among users. One typical communications system is the Local AreaNetwork (LAN) that interconnects a plurality of computer workstationusers. Perhaps the most common way in which computers or other devicesare connected together in a LAN is through electrically conductivewires. For example, wall or floor connectors may be located throughout abuilding to which computer workstations are connected, and metal wiresare run from the wall connectors to one or more central locations wherethey may be connected to centralized computing devices, such as aserver.

Certain disadvantages may accompany the use of wired networks. Forinstance, because electrical power is being transmitted over the wires,the installation of the wires may be subject to electrical codes thatmay make installation more difficult or even costly. Furthermore, thebandwidth that is available using typical metal wires (e.g., copperwires) may be less than desirable for some applications.

As a result of such limitations, other types of interconnections havebeen utilized in an attempt to provide “copperless” networks. Forexample, fiber-optic lines allow light signals which correspond toelectrical signals to be transmitted between computers or other devicesat a very high rate and bandwidth. Yet, fiber-optic communication isoften more expensive than wires, and thus running fiber-optic lines tonumerous wall connectors may be cost prohibitive in some circumstances.

Further, fiber-optic cables may be more difficult to extract signalsfrom than wires. As a result, various approaches for addressing thedifficulties of signal extraction from optical fibers have beendeveloped. One such approach is disclosed in U.S. Pat. No. 6,265,710 inwhich light emerging from an optical fiber is directed by focusingelements at a photodetector or at the input face of another glass fiber.Another approach is to use gratings which are physically configured tocapture light of a particular wavelength. An example of this approach isdisclosed in U.S. Pat. No. 6,304,696 to Patterson et al.

Another way to interconnect one or more devices in a LAN is to usewireless communications links. For example, each device in the LAN mayinclude a wireless radio frequency (RF) transceiver for sending andreceiving data signals to other devices using one or more designatedfrequencies. While this approach has the advantage of requiring less, ifany, wall connectors than a wired or fiber-optical network, the wirelesscommunications links may be subject to interference, signal distortion,or signal loss as devices are moved to various locations.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of theinvention to provide a communication system that effectively uses theadvantages of optical fiber and wireless communication.

This and other objects, features and advantages in accordance with thepresent invention are provided by a communication system including anoptical fiber, and at least one optical-wireless device coupled to aoptical fiber. By way of example, the at least one optical-wirelessdevice may be coupled to the fiber by standard fiber connectors,microfabrication of grating structures within the fiber, surfacepolished fiber to serve as an electronic substrate, etc. Moreover, theoptical-wireless device may include an optical fiber power unit coupledto the optical fiber for converting optical power therein intoelectrical power, and a wireless communication unit electrically poweredby the optical fiber power unit and coupled to the optical fiber. Theoptical-wireless device may include a substrate mounting the opticalfiber power unit and the wireless communication unit to the longitudinalside of the optical fiber.

The optical fiber power unit may include a photovoltaic device and apower optical grating coupling the photovoltaic device to thelongitudinal side of the optical fiber. The wireless communication unitmay include a radio frequency transmitter, and a signal optical gratingcoupling the transmitter to the longitudinal side of the optical fiber.

In accordance with another important aspect of the invention, the radiofrequency transmitter may be an ultra-wideband transmitter. Theultra-wideband transmitter, in turn, may include an optical detectorhaving an input coupled to the signal optical grating; an amplifierhaving an input connected to the output of the optical detector; apseudorandom code generator; a multiplier having inputs connected to theoutputs of the amplifier and pseudorandom code generator; and a pulsegenerator having an input connected to the output of the multiplier.

The ultra-wideband transmitter may also include an antenna connected tothe output of the pulse generator. By way of example, the antenna may bea dipole antenna. For a particularly compact and efficient construction,the dipole antenna preferably includes first and second portionsextending in opposite directions along the longitudinal side of theoptical fiber.

The optical fiber may include a core and a cladding surrounding thecore. Accordingly, the optical fiber power unit and the wirelesscommunication unit may be coupled to the core of the optical fiber.

In those embodiments where the wireless communication unit includes awireless transmitter, the system may further include at least onewireless receiver spaced from the wireless transmitter and receivingsignals therefrom. Conversely, in those embodiments where the wirelesscommunication unit comprises a wireless receiver, the system may alsoinclude at least one wireless transmitter spaced from the wirelessreceiver and transmitting signals thereto. Of course, in yet otherembodiments, duplex communications may be provided.

The communication system is particularly applicable to copperlessnetworks. In these embodiments, the at least one optical-wireless devicemay be a plurality of optical-wireless devices coupled to the opticalfiber at spaced apart locations along the longitudinal side of theoptical fiber. In some situations, a plurality of optical-wirelessdevices can be coupled to the optical fiber.

Different optical wavelengths may be used for powering and signals inthe optical-wireless device. More particularly, the wirelesscommunication unit may operate at a first optical wavelength, and thesystem may include an optical power source coupled to the optical fiberfor powering the optical fiber power unit and operating at a secondwavelength different than the first optical wavelength. Additionally,instead of different optical wavelengths, the optical-wireless devicescould also operate from different modes, polarizations, codes, orotherwise differentiate signals and power between the optical-wirelessdevices.

A method aspect of the invention is for optical-wireless communication.The method may include coupling at least one optical-wireless device toa longitudinal side of an optical fiber, where the at least oneoptical-wireless device may include an optical fiber power unit and awireless communication unit connected thereto. The method may alsoinclude supplying optical power into the optical fiber, converting theoptical power in the optical fiber into electrical power using theoptical fiber power unit, and electrically powering the wirelesscommunication unit for optical-wireless communication using theelectrical power converted from the optical power. In addition, externalpower could be supplied by methods such as solar cells, rectifyingantennas, or by electrical wire, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a communication system according to thepresent invention including a plurality of optical-wireless devicescoupled to an optical fiber.

FIG. 2 is partial cross-sectional view illustrating one embodiment of anoptical-wireless device and the optical fiber of FIG. 1 in greaterdetail.

FIG. 3 is a schematic block diagram of an ultra-wideband transmitter andpower generation circuitry therefor for the optical-wireless device ofFIG. 2.

FIG. 4 is a perspective view illustrating mounting of an alternatearrangement of the optical-wireless device of FIG. 2 on the opticalfiber.

FIG. 5 is a schematic block diagram illustrating communications betweenan optical-wireless device according to the invention including anultra-wideband transmitter and a receiver.

FIG. 6 is a schematic block diagram illustrating communications betweena transmitter and an optical-wireless device according to the inventionincluding an ultra-wideband receiver.

FIG. 7 is a flow diagram illustrating a method according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime notation is used toindicate similar elements in alternative embodiments.

Referring initially to FIG. 1, a communication system 10 according tothe present invention illustratively includes an optical fiber 11, andat least one optical-wireless device 12 coupled to a point(s) along alongitudinal side of the optical fiber. In the context of a LAN, forexample, the optical fiber 11 may be connected to a server 16 or othercentral data source/node to which electronic devices such as personaldata assistants 13, cellular telephones 14, and/or personal computers(PCs) 15 require access. Of course, those of skill in the art willappreciate that the communication system 10 of the present invention maybe used in numerous other applications other than LANs, and also withother types of electronic devices.

As such, those of skill in the art will appreciate that thecommunication system 10 is particularly applicable to copperlessnetworks. In such embodiments, a plurality of optical-wireless devices12 a, 12 b, 12 c may be coupled to the optical fiber 11 at spaced apartlocations along the longitudinal side of the optical fiber. Theoptical-wireless devices 12 a, 12 b, 12 c are used for respectivelyproviding wireless communications with the personal data assistant 13,the cellular telephone 14, and the personal computer (PC) 15. As will bediscussed more fully below, the optical-wireless device 12 mayadvantageously be used to convert optical signals sent on the opticalfiber 11 (e.g., by the server 16) to wireless signals and transmit thesame to a respective electronic device. Conversely, the optical-wirelessdevice 12 may also convert wireless signals sent from a respectiveelectronic device to corresponding optical signals and send the same onthe optical fiber 11 (e.g., to the server 16), as illustratively shownwith arrows in FIG. 1.

As a result of the optical-wireless device 12 of the present invention,the communication system 10 may advantageously realize certainadvantages of both optical and wireless communications while avoidingsome of their respective drawbacks. More particularly, one or moreoptical fibers 11 may be used to route signals from a server 16 or othercentral data source throughout an entire physical network area (e.g., afloor of a building, a ship, etc.) without having to run optical fibersto numerous workstation connection points.

Further, because optical signals can travel relatively long distancesover optical fibers with minimal degradation, the range over which thecommunication system 10 extends may be much larger than that of a purelywireless network, and may even extend between buildings, etc., withoutthe need for wireless signal repeaters. Plus, since the wireless signalstransmitted between the optical-wireless device 12 and a respectiveelectronic device generally do not have to travel as far as in a purelywireless network (i.e., they only have to travel to the nearby opticalfiber 11 and not all the way to the server 16), interference and signaldegradation may potentially be reduced as well.

Turning now more particularly to FIGS. 2-4, the optical-wireless device12 will now be described in greater detail. The optical fiber 11 mayinclude a core 23 and a cladding 24 surrounding the core, as will beappreciated by those of skill in the art. The optical-wireless device 12may include an optical fiber power unit 20 coupled to the core 23 forconverting optical power therein into electrical power, as will bedescribed further below.

Further, a wireless communication unit 25 may also be coupled to thecore 23 of the optical fiber 11 and electrically powered by the opticalfiber power unit 20. In some embodiments, such as the one illustrated inFIG. 2, portions of the optical fiber power unit 20 and the wirelesscommunication unit 25 may be embodied in a single integrated device. Adotted line is therefore shown in FIG. 2 to aid in illustrating that thetwo separate functions are performed in the same optical-wireless device12, although no particular segmentation or arrangement of the variouscircuit components is required.

The optical fiber power unit 20 may include one or more photovoltaicdevices 21 and a respective power optical grating 22 designedspecifically to extract light from the core 23 of the optical fiber 11to be used for power generation. As such, the power optical grating 22is preferably “tuned” to extract light having a particular opticalwavelength λ₁ from the core 23, which is converted to electrical powerfor the wireless communications device 25. As will be appreciated bythose skilled in the art, a micro-optic structure to extract light forpower generation may be “tuned” to specific wavelengths, polarizations,modes, etc. The optical fiber power 20 unit 20 may optionally includeadditional power conditioning circuitry as required, as will beappreciated by those of skill in the art, which is schematically shownin FIGS. 5 and 6.

By way of example, one particular type of photovoltaic device 21 whichmay be used is a relatively large-area planar-diffused InGaAs photodiodewith a broadband anti-reflection coating on the photosensitive surface.Such diodes are known to those of skill in the art. Several suchphotovoltaic diodes 21 may be connected in series (illustratively shownin FIGS. 5 and 6) to generate the requisite voltage to power thewireless communication unit 25 and reverse bias an optical signaldetector 26 thereof (discussed further below). The photodiodes 21 arepreferably placed over respective gratings 22 in a manner that optimizesthe illumination efficiency.

As will be appreciated by those of skill in the art, to optimize theillumination efficiency of a photodiode it is important to have themaximum amount of light extracted from the core 23 absorbed within thedepletion region of the photodiode 21. Light extracted from the core 23and not absorbed in the depletion region represents loss and a reductionin efficiency. Losses can result from reflections, misdirected ormisfocused light, and absorption of photons outside the depletionregion. Anti-reflection coatings, junction orientation, and beamfocusing may be tailored in a particular design application to minimizelosses, as will also be appreciated by those skilled in the art.

One exemplary approach for illuminating a photodiode 21 is to have thelight incident normal to the photodiode junction. An alternate approachwould be to have the incident light parallel to the photodiode 21junction. The latter approach has the advantage of aligning the junctionalong the length of the core 23. This may accommodate longer gratings 22with enhanced functionality, for example. Other approaches maypotentially be used as well, as will be understood by those skilled inthe art.

It will also be understood that for maximum power delivery to a loadfrom a power source, load resistance and equivalent source resistance ispreferably made equal. Under illumination, a photodiode connected to anopen circuit load will produce a photovoltage, V_(OC). Likewise, aphotodiode connected to a short circuit load will produce aphotocurrent, ISC. The equivalent source resistance, REQ, of thephotodiode is then approximately V_(OC)/I_(SC). To optimize powerdelivery to the optical-wireless device 12, the source resistance andload resistance should preferably be tailored in each particularapplication to achieve an optimal match, as will be appreciated by thoseskilled in the art.

In addition to optimizing illumination of the photodiodes, parasiticimpedances introduced by the packaging into the electrical interconnectshould preferably be held to a minimum. Parasitic resistance in thepower source conductors will decrease power conversion efficiency, aswill be appreciated by those of skill in the art. Care may also need tobe taken to ensure that parasitic impedances between the transmitter 27and antenna 34 (FIG. 3) do not overly limit the bandwidth and/or shapeof the radiated pulses. Various types of interconnections may be used inaccordance with the present invention, and potential criteria for theselection thereof are that they should be simple, inexpensive, andaccommodate mass production.

One such approach for forming the electrical interconnections is to useconductive epoxy. Forming interconnections in this manner is well knownin the art, has lower parasitic inductance than wire bonding, andoccupies less physical space than other conventional interconnections.The same epoxy forming the interconnect can also permanently hold thedevices in place. In addition, additives can be used to alter theconductivity of the epoxy to form a resistor 39 (FIG. 3) used to biasthe signal detecting diode 26. This is possible because of the very lowpower requirements of the biasing resistor 39 in the signal detectorcircuit. Further, non-conductive epoxy 44 may be used to isolate thephotodiodes 21 form the signal detecting diode(s) 26.

Multifunctional use of epoxy may reduce package complexity, size, thenumber of process steps required for assembly, and cost. Where wirebonds are more appropriately used, the parasitics associated therewithare preferably held to a minimum. Wire bonds can easily introducenano-Henry level inductances into the package if care is not taken. Onemethod to reduce the parasitics of a wire bond is to press the bond flattoward the package 19 or substrate 43 (FIG. 4) This limits the wirecurvature to reduce flux linkage, and brings the wire closer to theground plane to act more as a transmission line with controlledimpedance.

In particular, wire bonds 40 may be used for coupling the photodiodes 21in series, as described above, and wire bonds 41 may be used forcoupling the optical power fiber unit 20 to the wireless communicationsunit 25. Additionally, wire bonds 42 a, 42 b may be used for couplingthe wireless communications unit 25 to the dipole antenna elements 34 a,34 b (FIG. 1).

The wireless communication unit 25 may include a radio frequency (RF)transmitter 27, and an optical signal grating 28 optimized forextracting optical data signals from the fiber 11. Of course, theoptical signal grating 28 and power grating 22 may be optimizeddifferently. According to one important aspect of the invention, the RFtransmitter 27 may be an ultra-wideband (UWB) transmitter. UWB provideswireless communications spread to very low power spectral density acrossa very wide band of frequencies. Data is transmitted by modulating andradiating discrete pulses of RF energy. As a result, UWB may beparticularly advantageous for use in the communication system 10 becauseit may coexist with many existing continuous wave narrowband systemswithout interference. Furthermore, the broad spectral nature and/or lowfrequency content of UWB pulses makes it better suited to penetratewalls and obstacles than other existing technologies. Of course, thoseof skill in the art will appreciate that other forms of wirelesscommunication may also be used in accordance with the present invention.

As illustratively shown in FIG. 3, for example, the ultra-widebandtransmitter 27 may include an optical signal detector 26 having an inputcoupled to the signal optical grating (FIG. 2). The signal detector 26may also be a photodiode, such as the InGaAs photodiode described above.The same considerations described above with respect to placement,efficiency, etc. of the photodiodes 21 is also applicable to thephotodiode 26, and will therefore not be discussed further here exceptto note that typically only one photodiode 26 is required for signaldetection (although more may be used). Further, optional signalconditioning circuitry (not shown) may also be included in someembodiments which, in those embodiments where the wireless communicationunit 25 is implemented using semiconductor technology, may beimplemented using the same technology.

An amplifier 30 has an input connected to the output of the opticaldetector 26. The transmitter further includes a pseudorandom codegenerator 31, a multiplier 32 having inputs connected to the outputs ofthe amplifier 30 and the pseudorandom code generator, and a pulsegenerator 33 having an input connected to the output of the multiplier.Other UWB transmitter circuitry arrangements are also possible, as willbe understood by those of skill in the art.

The ultra-wideband transmitter 27 may also include an antenna 34connected to the output of the pulse generator 33. By way of example,the antenna 34 may be a dipole antenna connected to the ultra-widebandtransmitter 27 (or other suitable RF device) by wire bonds 42 a, 42 b(FIG. 1). For a particularly compact and efficient construction, thedipole antenna 34 preferably includes first and second portions 34 a, 34b extending in opposite directions along the longitudinal side of theoptical fiber 11, as illustratively shown in FIG. 2.

To maintain a low profile, it would be preferable to use a broadbanddipole antenna 34 that can be integrated onto the side of the opticalfiber. Yet, as will be appreciated by those of skill in the art, mostdipole antennas have an inherently narrow band because they are resonantstructures that support standing waves. Accordingly, various approachesmay be used to increase the bandwidth of the dipole antenna 34 tosupport ultra-wideband transmission more efficiently. One such approachis the traveling wave approach, in which the current distribution in theantenna is altered so that it supports a traveling wave.

More particularly, the amplitude of the current wave is made to decreasewith distance away from the input terminals by using a resistivematerial to form the dipole. The antenna 34 may be truncated at thepoint where the current distribution becomes negligible withoutsignificantly affecting the performance of the antenna. With very littlecurrent to reflect from the dipole endpoints, resonance is avoided andthe structure supports traveling waves. This approach improvesbandwidth, but potentially at the cost of efficiency due to dissipativelosses in the antenna 34. It will be appreciated by those skilled in theart that the resistance profile of the antenna 34 may need to be variedalong its length to optimize the trade-off between efficiency andbandwidth in some applications. Further information regarding thisapproach may be found in Tonn et al., “Traveling Wave Microstrip DipoleAntennas”, I.E.E.E., Electronics Letters, volume 31, issue 24, Nov. 23,1995, pages 2064 to 2066.

Yet another approach is that of impedance loading, which purposelyintroduces parasitics to broaden the frequency response by making theeffective length of the dipole frequency dependent. This is accomplishedby preventing higher frequencies from having multiple resonances andconfining them to a smaller portion of the dipole. Here again, thisapproach may improve bandwidth at the cost of efficiency due todissipative losses in the parasitic loads. Thus, the impedance profileof the antenna 34 may need to be varied along its length to optimize thetrade-off between efficiency and bandwidth in some applications. Furtherinformation on this approach may be found in “Numerical modeling anddesign of loaded broadband wire antennas” by Austin et al., I.E.E.E,Fourth International Conference on HF Radio Systems and Techniques,1988, pages 125 to 129.

Accordingly, those skilled in the art may be required to determine whichof the above approaches (or others) may be best suited for a particularimplementation of the present invention. Furthermore, the impedanceand/or resistance profile of the antenna can be tailored for reasonsother than bandwidth and efficiency. The profile can be designed andoptimized for functions such as pulse shaping and signal filtering.

As noted above, in accordance with one aspect of the present invention,the power optical grating 22 is used for extracting light from the core23 to power the wireless communications unit 25, and the optical signalgrating 28 is used to either extract light from (in the case of signaltransmission from the wireless communications unit) or introduce lightinto (i.e., in the case of signal reception by the wirelesscommunications unit) the core. Of course, those of skill in the art willappreciate that other approaches exist for extracting light from anoptical fiber 11, such as evanescent coupling, power splitting, or evenmultiple fibers. Such approaches, as well as other suitable approachesknown to those skilled in the art, are also included within the scope ofthe present invention.

Preferably, different optical wavelengths are used for powering andsignals in the optical-wireless device 12. More particularly, thewireless communication unit 25 may operate with light having an opticalwavelength λ₂, which is provided (in the case of transmission by thewireless communication unit) by an optical signal source 35 (FIG. 5). Insuch case, the optical signal grating 28 is “tuned” to λ₂, as will bediscussed further below. Further, the communication system 10 mayinclude an optical power source 36 coupled to the optical fiber, and,more particularly, the core 23, for powering the optical fiber powerunit 20 using light having the wavelength λ₁, as noted above. Of course,in some embodiments it may be possible to extract both signals and powerfrom a single source of light having the same wavelength. The opticalpower source 36 and the optical signal source 35 may be circuitryinternal to the server 16, for example.

Fabrication of the gratings 22 and 28 will now be discussed in furtherdetail. To facilitate the fabrication process, a fiber bench 29 mayadvantageously be used. A fiber bench is a section of fiber where aportion of the cladding 24 is polished away to form a flat surface inclose proximity to the fiber core 23. It will be appreciated by thoseskilled in the art that the surface gratings 22, 28 fabricated on thefiber bench 29 can exploit the evanescent field to perform a variety offunctions such as spectral filtering, dispersion compensation, modematching, mode stripping, or light extraction and injection. Thegratings 22, 28 can also be designed to perform these functions overselected wavelengths (e.g., λ₁ and λ₂) or modes, while not affectingothers.

Interfacing with the optical fiber 11 in this manner has the advantagesof lower insertion loss, reduced system complexity, enhancedfunctionality, and the potential for volume production. A conventionalsplice might otherwise suffer from higher losses in the optical fiber 11when using multiple optical-wireless devices 12 operating from differentwavelengths. The fiber bench 29 can also be used as a micro-sizedsubstrate to host small devices such as MEMS, sensors (e.g.,bio/chemical, acoustic, seismic, etc.), or other microsystems in certainembodiments.

The fiber bench 29 can be formed by placing the fiber in a siliconV-groove and filling the gaps with an epoxy. With the epoxy cured, theentire assembly is polished until the cladding 24 of the optical fiber11 is within close proximity to the core 23. A liquid drop testmeasurement may then be used to accurately control the proximity of thefiber bench 29 surface to the fiber core 23. The process may beautomated, and systems with fiber benches can potentially be massproduced at low cost. For further details on the use of fiber benches,see, e.g., Leminger and Zengerle, Journal of Lightwave Technology,Volume 3, 1985.

Additional benefits of this approach include the ability to use thesilicon bench 29 portion of the device for integration with detectorelectronics. Moreover, it is feasible that additional optics and/orantenna elements (not shown) can be integrated on the silicon portion ofthe fiber bench 29, as will be appreciated by those of skill in the art.

The liquid drop test measurement method assesses the proximity of thefiber bench 29 surface to the core 23 of the optical fiber 11. Light isinjected into one end of the optical fiber 11 so that it propagatesthrough the region of the fiber bench 29 and eventually to a powermeter. By placing a drop of liquid on the fiber bench 29 surface, lightis outcoupled in the region of the liquid and can be measured by thepower meter as loss. The fraction of light lost can be used to computethe distance from the bench surface to the core of the fiber.

One approach for fabricating the gratings 22, 28 involves tilting thecore 23 during the formation thereof. As will be understood by those ofskill in the art, gratings are inherently spectrally selective due totheir dispersive properties, and can be designed to selectively redirectbands of wavelengths out of the core 23. The outcoupled light would besubsequently focused onto the photodiodes 21, 26 using micro-opticalelements fabricated on the flat side of the optical fiber 11. Since thisapproach requires photosensitive glass to produce the gratings 22, 28adjacent the core 23, a strong variation in the index may be difficultto realize. A low index modulation requires a long interaction length tocouple large amounts of optical power out of the fiber. This maycomplicate focusing and limit micropackaging options.

Accordingly, standard lithographic processes may be used to fabricatethe surface gratings 22, 28 by etching them onto the polished surface ofa optical fiber 11. To reduce the interaction length, the indexmodulation may be greatly enhanced by applying a higher index materialovercoat on the surface of the grating structure.

Tilted surface grating structures may also potentially be used tooptimize light extraction and photodiode illumination efficiency. Thiscan be achieved by placing the optical fiber 11 on a tilted fixture andusing an anisotropic etch pattern on the fiber bench 29 surface. Thisapproach can yield slant angles from 0 to 30 degrees, for example. Toavoid the need for additional focusing optics, the interaction length ofthe grating structures 22, 28 is preferably no longer than the activeregions of their respective photodiodes 21, 26. In this manner, theoutcoupled light will be inherently confined to the area of the activeregion. If additional focusing becomes necessary, diffractive optics maybe used to focus light onto the photodiodes 21, 26, as will beunderstood by those skilled in the art.

The above approach for extracting light is based on redirecting, ortapping, the guided light out of the optical fiber 11 from specificwavelengths, or modes, for power and signal extraction. An alternateapproach views the problem as a spectrally selective directionalcoupler. The fiber core 23 and the photodiode substrate represent thetwo regions for light to propagate. By bringing these two regions inclose proximity, it is possible to couple light from the fiber to thephotodiode very efficiently by designing a spectrally selective gratingto match the propagation constants of these two regions, effectivelyforming a directional coupler, as will be appreciated by those of skillin the art.

As noted above, light for signals and power may be provided on differentwavelengths λ₁, λ₂ and, using the wavelength selective gratings 22, 28,the power and signal light can thereby be extracted separately. Analternate approach is to provide the light for signals and power ondifferent propagating modes. For example, a process has been developedwhich uses a vortex lens to excite specific modes of a graded-indexmultimode which may be suitable for this purpose. This process isdescribed by Johnson et al. in “Diffractive Vortex Lens forMode-Matching Graded Index Fiber,” Optical Society of America, TopicalMeeting on Diffractive and Micro-Optics, 2000. Therefore, it may also befeasible to use diffractive optics to specifically launch light intodifferent spatial modes for the power and signal wavelengths λ₁, λ₂, aswill be appreciated by those skilled in the art. Correspondingly, itwill also be appreciated that diffractive optics may potentially bedesigned for spatially demultiplexing the power and signal modes,respectively.

Another approach is to utilize a duplex fiber assembly with one fiberdevoted to providing power and the other fiber for signal distribution.This will have some advantages in that the power channel can beamplified, or re-supplied, at various places in the network, withoutinterrupting the signal fiber. In this manner, the power source can bedistributed, which may make the communication system 10 more reliableand robust. Moreover, the optical fiber 11 can be used with wavelengthdivision multiplexing (WDM) or dense WDM (DWDM) schemes, for example, aswill be appreciated by those of skill in the art. This approach candistribute the different signals using standard passive WDM technologyand standard amplifier technology for the power channel. However, thisintegration potentially requires a larger amount of real estate than thesingle optical fiber approach disclosed above. Of course, it will beappreciated that both embodiments are included within the scope of thepresent invention, and that a separate conductive wire could even beused to provide power in some embodiments.

As noted above, portions of the optical-wireless device mayadvantageously be implemented in a semiconductor device having apackaging 19 (FIG. 2). In this embodiment, the packaging 19 may serve asa substrate for mounting the optical fiber power unit 20 and thewireless communication unit 25 to the longitudinal side of the opticalfiber 11. In the embodiment illustrated in FIG. 4, a separate substrate43 (e.g., a ceramic substrate) may be used for this purpose as well.

One potential micropackaging approach illustrated in FIG. 4 involvesmaking the various hardware portions modular. More particularly, a rowof photodiodes 21, 26 is fixed to the front side of the ceramicsubstrate 43. The back side of the substrate 43 is populated with theUWB radio hardware described above. Electrical interconnection isprovided by conductive and resistive epoxies, metal traces in theceramic substrate, and wire bonds, as also noted above. In thisconfiguration, the ceramic and silicon substrates could be “snapped”together, for example.

It was also noted above that the optical-wireless unit 12 may bothtransmit and receive wireless signals. In those embodiments where thewireless communication unit 12 includes a wireless transmitter 27, thecommunication system 10 may further include at least one wirelessreceiver 37 (and associated antenna 38) spaced from the wirelesstransmitter and receiving signals therefrom, as illustratively shown inFIG. 5. Conversely, in those embodiments where the wirelesscommunication unit 12 includes a wireless receiver, the system may alsoinclude at least one wireless transmitter 60′ (and associated antenna61′) spaced from the wireless receiver and transmitting signals thereto.Of course, in yet other embodiments, duplex communications may beprovided, i.e., the wireless communications unit 12 may include atransceiver, for example.

Turning now to FIG. 7, a method aspect of the invention foroptical-wireless communication will now be described. The method maybegin (Block 70) with coupling, at Block 71, at least oneoptical-wireless device 12 to a longitudinal side of an optical fiber11, with the at least one optical-wireless device including an opticalfiber power unit 20 and a wireless communication unit 25 connectedthereto, as previously described above. The method may also includesupplying optical power into the optical fiber 11, at Block 72,converting the optical power in the optical fiber into electrical powerusing the optical fiber power unit 20, at Block 74, and electricallypowering the wireless communication unit 25 for optical-wirelesscommunication using the electrical power converted from the opticalpower, at Block 73, thus concluding the method (Block 75). Additionalmethod aspects will be understood from the above description and willtherefore not be discussed further herein.

It will therefore be appreciated by those of skill in the art thatnumerous advantages are provided by the communication system 10 of thepresent invention. In particular, these advantages may include: seamlessconversion between optical and wireless domains; reliable, untethered,and high capacity access to optical links; the potential benefits ofultra-wideband impulse radio; a high degree of covertness; a smallcompact form factor; distributing wireless node functionality along theoptical fiber 11 without optical-electrical-optical splices; moresurvivable systems due to added redundancy; more mobile systems that areeasier to manage than conventional optical-to-wireless systems; lesscomplex systems than conventional optical-to-wireless converters;cabling minimization; systems that may be rapidly deployed at low cost;copperless LANs that are easier and quicker to install than conventionaloptical-to-wireless systems; significant increase in the reach of“conventional” UWB links and ad-hoc networks; latency and processingoverhead may be substantially eliminated at optical/wirelessinterworking points; frequency allocation restraints may be bypassed;and system costs may be reduced.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that modificationsand embodiments are intended to be included within the scope of theappended claims.

1. A communication system comprising: an optical fiber comprising a core and a cladding surrounding said core; a fiber bench having a groove retaining said optical fiber therein; said optical fiber having a portion of said cladding removed to define an exposed core portion flush with adjacent portions of said fiber bench; and at least one optical-wireless device coupled to a longitudinal side of said optical fiber adjacent the exposed core portion and comprising an optical fiber power unit coupled to said exposed core portion for converting optical power therein into electrical power, and a wireless communication unit electrically powered solely by said optical fiber power unit and coupled to said exposed core portion and comprising an ultra-wideband transmitter and a signal optical grating coupling said ultra-wideband transmitter to the longitudinal side of said optical fiber, said ultra-wideband transmitter comprising an optical detector having an input coupled to said signal optical grating and having an output, an amplifier having an input connected to the output of said optical detector and having an output, a pseudorandom code generator having an output, a multiplier having inputs connected to the outputs of said amplifier and pseudorandom code generator, and having an output, a pulse generator having an input connected to the output of said multiplier, and having an output, and an antenna connected to the output of said pulse generator.
 2. A communication system according to claim 1 wherein said at least one optical-wireless device further comprises a substrate mounting said optical fiber power unit and said wireless communication unit to the longitudinal side of said optical fiber.
 3. A communication system according to claim 1 wherein said optical fiber power unit comprises a photovoltaic device and a power optical grating coupling said photovoltaic device to the longitudinal side of said optical fiber.
 4. A communication system according to claim 1 wherein said antenna comprises a dipole antenna.
 5. A communication system according to claim 4 wherein said dipole antenna comprises first and second portions extending in opposite directions along the longitudinal side of said optical fiber.
 6. A communication system according to claim 1 wherein said wireless communication unit comprises a wireless transmitter; and further comprising at least one wireless receiver spaced from said wireless transmitter and receiving signals therefrom.
 7. A communication system according to claim 1 wherein said wireless communication unit comprises a wireless receiver; and further comprising at least one wireless transmitter spaced from said wireless receiver and transmitting signals thereto.
 8. A communication system according to claim 1 wherein said at least one optical-wireless device comprises a plurality of optical-wireless devices coupled to said optical fiber at spaced apart locations along the longitudinal side of said optical fiber.
 9. An optical-wireless device to be coupled to a longitudinal side of an optical fiber, the optical fiber comprising a core and a cladding surrounding the core, and a fiber bench having a groove retaining the optical fiber therein, the optical fiber having a portion of the cladding removed to define an exposed core portion flush with adjacent portions of the fiber bench, the optical-wireless device comprising: a substrate for coupling to the longitudinal side of the optical fiber adjacent the exposed core portion; an optical fiber power unit carried by said substrate to be coupled to said exposed core portion for converting optical power therein into electrical power; and a wireless communication unit carried by said substrate, solely electrically powered by said optical fiber power unit, and to be coupled to the exposed core portion and comprising an ultra-wideband transmitter and a signal optical grating coupling said ultra-wideband transmitter to the longitudinal side of said optical fiber said ultra-wideband transmitter comprising an optical detector having an input coupled to said signal optical grating and having an output, an amplifier having an input connected to the output of said optical detector and having an output, a pseudorandom code generator having an output, a multiplier having inputs connected to the outputs of said amplifier and pseudorandom code generator, and having an output, a pulse generator having an input connected to the output of said multiplier, and having an output, and an antenna connected to the output of said pulse generator.
 10. An optical-wireless device according to claim 9 wherein said optical fiber power unit comprises a photovoltaic device and a power optical grating for coupling said photovoltaic device to the optical fiber.
 11. An optical-wireless device to be coupled to an optical fiber and comprising: a substrate to be directly coupled to the optical fiber; a signal optical grating; and an ultra-wideband wireless communication unit carried by said substrate and to be coupled to the optical fiber, the ultra-wideband wireless communications unit comprising an ultra-wideband transmitter comprising an optical detector having an input coupled to said signal optical grating and having an output, an amplifier having an input connected to the output of said optical detector and having an output, a pseudorandom code generator having an output; a multiplier having inputs connected to the outputs of said amplifier and said pseudorandom code generator, said multiplier also having an output, a pulse generator having an input connected to the output of said multiplier, and having an output, and an antenna to be carried by the optical fiber and connected to the output of said pulse generator; said signal optical grating for coupling said ultra-wideband transmitter to the optical fiber.
 12. An optical-wireless device according to claim 11 wherein said substrate is to be coupled to a longitudinal side of the optical fiber.
 13. An optical-wireless device according to claim 11 wherein said antenna comprises a dipole antenna.
 14. An optical-wireless device according to claim 13 wherein said dipole antenna comprises first and second portions to extend in opposite directions along the longitudinal side of the optical fiber.
 15. A communication system comprising: an optical fiber; at least one optical-wireless device coupled to a longitudinal side of said optical fiber and comprising an optical fiber power unit coupled to said optical fiber for converting optical power therein into electrical power, and a wireless communication unit electrically operating at a first optical wavelength powered by said optical fiber power unit and coupled to said optical fiber; and an optical power source coupled to said optical fiber for powering said optical fiber power unit and operating at a second wavelength different than the first optical wavelength.
 16. A communication system according to claim 15 wherein said at least one optical-wireless device further comprises a substrate mounting said optical fiber power unit and said wireless communication unit to the longitudinal side of said optical fiber.
 17. A communication system according to claim 15 wherein said optical fiber power unit comprises a photovoltaic device and a power optical grating coupling said photovoltaic device to the longitudinal side of said optical fiber.
 18. A communication system according to claim 15 wherein said wireless communication unit comprises a radio frequency transmitter and a signal optical grating coupling said radio frequency transmitter to the longitudinal side of said optical fiber.
 19. A communication system according to claim 18 wherein said radio frequency transmitter comprises an ultra-wideband transmitter.
 20. An optical-wireless device to be coupled to an optical fiber and comprising: a substrate to be coupled to the optical fiber; and an ultra-wideband transmitter and a signal optical grating both carried by said substrate, said optical grating for coupling said ultra-wideband transmitter to the optical fiber, said ultra-wideband transmitter comprising an optical detector having an input coupled to said signal optical grating and having an output, an amplifier having an input connected to the output of said optical detector and having an output, a pseudorandom code generator having an output, a multiplier having inputs connected to the outputs of said amplifier and said pseudorandom code generator, said multiplier also having an output, a pulse generator having an input connected to the output of said multiplier, and having an output, and an antenna to be carried by the optical fiber and connected to the output of said pulse generator.
 21. An optical-wireless device according to claim 20 wherein said substrate is to be coupled to a longitudinal side of the optical fiber.
 22. An optical-wireless device according to claim 20 wherein said antenna comprises a dipole antenna.
 23. An optical-wireless device according to claim 22 wherein said dipole antenna comprises first and second portions to extend in opposite directions along the longitudinal side of the optical fiber.
 24. A method for optical-wireless communication via an optical fiber comprising a core and a cladding surrounding the core, the method comprising: coupling at least one optical-wireless device to a longitudinal side of the optical fiber by the cladding, the at least one optical-wireless device comprising an optical fiber power unit and a wireless communication unit connected thereto, the wireless communication unit operating at a first optical wavelength; supplying optical power at a second wavelength different than the first optical wavelength into the optical fiber using an optical power source; converting the optical power in the optical fiber into electrical power using the optical fiber power unit; and electrically powering the wireless communication unit for optical-wireless communication using the electrical power converted from the optical power.
 25. A method according to claim 24 wherein the optical-wireless device further comprises a substrate carrying the optical fiber power unit and the wireless communication unit; and wherein coupling comprises coupling the substrate to the longitudinal side of the optical fiber.
 26. A method according to claim 24 wherein the wireless communication unit comprises a radio frequency transmitter and a signal optical grating coupling the radio frequency transmitter to the longitudinal side of the optical fiber.
 27. A method according to claim 26 wherein the radio frequency transmitter comprises an ultra-wideband transmitter. 